1. Field of the Invention
The present invention relates to a light-emitting diode lamp (hereinafter abbreviated as an “LED lamp”), wherein a plurality of light-emitting elements, a wiring sub-mount for electrically interconnecting the light-emitting elements, and a wire are housed in a case made of synthetic resin or the like and sealed with material, such as translucent, transparent epoxy resin. Throughout the specification, an LED chip itself is called a “light-emitting element,” and the entirety of a light-emitting device having a plurality of LED chips mounted thereon is called a “light-emitting diode lamp” or an “LED lamp.”
2. Description of the Related Art
At the time of designing of an LED-applied product, in terms of optics it is preferable to design an LED so as to become as much close to a point light source as possible. Miniaturization of an LED lamp into an SMD (Surface Mount Device)-type package, such as a 2-in-1 (two light-emitting elements are housed in one package), a 3-in-1 (three light-emitting elements in one package), and a 4-in-1 (four light-emitting elements are housed in one package) has been under study.
When an attempt is made to connect a plurality of GaN-based light-emitting elements in series and seal the elements in a single package, a plurality of gold wires for interconnection purpose are required. Further, there is needed a space for interconnecting the gold wires, thus posing difficulty in miniaturization of the package. If an LED is miniaturized, the heatsinking performance of the LED will become worse. As a result, the light-emitting elements become hot, thus the worsening luminous efficiency of the LED lamp.
Further, the LED lamp of SMD package type has hitherto been employed as a light source for backlighting purpose. The lamp is manufactured by means of laying a plurality of metal leads in a case which is formed from synthetic resin through injection molding; connecting a plurality of light-emitting elements to one of the leads; electrically connecting the light-emitting elements to other leads through wire bonding; and sealing the entire case with transparent epoxy resin or the like. One example of such a related-art LED lamp will now be described by reference to FIGS. 12A, 12B, and 13.
As shown in FIG. 12A, an LED lamp 51 is constituted of a case 52 made of synthetic resin, and one metal lead 53 is inserted into an upper half of an opening section 52a of the case 52 and extends from the left end of the opening section 52a across to the right end thereof. A total of five light-emitting elements are mounted on the lead 53; namely, two red light-emitting elements R1, R2; two green light-emitting elements G1, G2; and one blue light-emitting element B1. Five leads 54a, 54b, 54c, 54d, and 54e are inserted into a lower half of the opening section 52a of the case 52 while being spaced away from the lead 53. The leads 53 and 54a through 54e and the case 52 are formed into one piece, by means of setting the leads 53 and 54a through 54e in a die to be used for injection molding the case 52, and subjecting the case 52 to insertion molding.
The five light-emitting elements are electrically connected together in the following manner. Since anode electrodes of the red light-emitting elements R1, R2 are provided on the reverse sides thereof, the red light-emitting elements R1, R2 are mounted on the lead 53 by means of a silver paste, whereby the anode electrodes of the red light-emitting elements R1, R2 are connected to the lead 53. Cathode electrodes of the red light-emitting elements R1, R2 are provided on the front side thereof. Hence, the element R1 is bonded to the lead 54a with a wire 55, and the element R2 is bonded to the lead 54e with a wire 55. Meanwhile, the GaN-based green light-emitting elements G1, G2 and the blue light-emitting element B1 have cathode and anode electrodes on their front sides. All the anode electrodes of the elements G1, G2, and B1 are bonded to lower projections of the lead 53 with wires 55. The cathode electrodes of the elements G1, G2, and B1 are bonded to the leads 54b, 54c, and 54d with wires 55. As shown in FIG. 12B, the opening section 52a of the case 52 is filled and sealed with transparent epoxy resin 56.
FIG. 13 shows electrical connection of the thus-connected five light-emitting elements in the form of a circuit diagram. As shown in FIG. 13, the LED lamp 51 has an anode common circuit which takes the lead 53 as an anode terminal. Such an electrical circuit enables a decrease in the number of terminals, thereby miniaturizing the LED lamp 51.
In relation to such an LED lamp, particularly an LED lamp for backlighting purpose, strong demand exists for an LED having a lower-profile opening of a case, a lower-profile of the outside shape of the lamp, higher intensity, and superior heatsink performance. In contrast, in order to realize an anode-common circuit, the related-art LED lamp 51 requires a large wire space. To this end, the thickness of the opening section (i.e., the longitudinal length) is made large. As shown in FIG. 12B, the lower leads 54a through 54e must be folded backward. At this time, if a portion 52b supporting the lead 54 of the case 52 is thin, the portion 52b becomes prone to cracking. Hence, the portion 52b supporting a lead must have a certain minimum thickness. Consequently, the entire outside shape of the case 52 has become thick. Since all the light-emitting elements R1, R2, G1, G2, and B1 are mounted on one lead 53, there is no alternative but to dissipate the heat produced by the light-emitting elements by way of the lead 53. Thus, the LED lamp involves a problem even in terms of heat dissipation.